Many types of input devices are available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens, and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens generally allow a user to perform various functions by touching (e.g., physical contact or near-field proximity) the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Mutual capacitance touch screens can be formed from a matrix of drive and sense lines of a substantially transparent conductive material such as Indium Tin Oxide (ITO). The drive and sense lines are often arranged orthogonally with respect to each other on a substantially transparent substrate and are configured to generate signals in response to a touch or proximity event.
Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Due to the mechanical architecture or configuration of a device incorporating the touch screen, an external force applied to the device can affect the touch signals in the touch sensor panel. The amount of force being exerted on the device can vary depending on how the user is holding device and other external environmental conditions. This dynamic force can create signal distortions on the touch sensor panel which can affect the ability of the panel to reliably detect touch and proximity events.